1. Field of the Invention
The invention relates to a bearing device for a threaded spindle, in particular, of a machine-tool, comprising a bearing housing having at least one receptacle which receives a bearing part of the threaded spindle.
2. Description of the Related Art
Threaded spindles of machine tools are known which are received with their ends in bearing devices and on which, for example, carriages are movable which are seated with at least one rotatably driven threaded nut on the threaded spindle. Upon longer operation of the machine tool, the threaded spindle will heat up so that longitudinal extensions occur which result in an impermissibly high loading or even damage of the bearing device.
Therefore, one end of the spindles is received in a fixed or locating bearing and the other end is received in a floating or non-locating bearing. Further measures include mechanical (spring) or fluid-operated pretensioning devices. These bearing arrangements, however, reduce as a whole the stiffness of the spindle which results in a tendency to vibrate and in loss of precision. Moreover, the systems are cost-intensive and complex with regard to their configuration and reduce the permissible operational load of spindles and bearings by the amount of pretensioning.
It is an object of the present invention to provide a bearing device of the aforementioned kind with which damages as a result of longitudinal extensions of the threaded spindle can be reliably prevented and which, during operation, exhibit the physical conditions of a spindle secured or fixed on both ends.
In accordance with the present invention, this is achieved in that the receptacle for the bearing part of the threaded spindle is a clamping bushing which for clamping the bearing part of the threaded spindle can be loaded by electro-mechanical or fluid-operated elements.
In the bearing device according to the invention the bearing part of the threaded spindle is clamped by a clamping bushing. The clamping bushing is loaded by electro-mechanical elements or fluid-operated elements so that it secures the bearing part and thus the threaded spindle by a frictional connection in the axial direction. The pressure medium in the clamping bushing is relieved pursuant to a temporal sequence or according to signals of a measuring device for measuring length changes or tension changes. This cancels the frictional connection between the clamping bushing and the bearing part of the threaded spindle. The extension which is caused by heating of the threaded spindle can thus be compensated. As soon as this length compensation has taken place, the pressure medium of the clamping bushing is again pressurized so that the high frictional connection acting in the axial direction between the clamping bushing and the bearing part of the threaded spindle is reinstated.